An Invercargill District Court judge yesterday took the rare step of directing a jury to find a woman not guilty, after it was revealed in court the woman's daughter may have lied about allegations she had made against her mother.

The woman, who has permanent name suppression, faced five charges of assaulting a child and two of assault with a weapon.

Her jury trial started yesterday before Judge Kevin Phillips.

The Crown had alleged the woman had assaulted her son and daughter, both aged under 10 years at the time, between August 2003 and February 2010.

In her opening address, Crown prosecutor Emma Riddell said the boy said in his evidential video interview his mother had hit him with a belt so hard his back had bled.

He also spoke of his mother smashing his sister's head into a wall, making it bleed, and leaving a dent in the wall, she said.

However, defence lawyer Kate McHugh said in her brief opening statement the defence case was that the allegations were untrue and the children had made the story up because they wanted to live with their father.

The children's father, whose name also cannot be revealed, told the jury his children had been living with him since February 2010, after staying with him for a few days during the holidays.

When their mother had come to pick them up, the boy had told him he did not want to leave, the father said.

The children had later told him something concerning, prompting him to contact a lawyer and Child, Youth, and Family, he said.

However, after being questioned by Ms McHugh, he also said his daughter later told him, following contact with her mother, that she had made the story up.

The Crown later offered no further evidence and Judge Phillips directed the jury to find the woman not guilty on all charges.